1. Technical Field
The present invention relates to an imaging device for taking an image of an object and a method of controlling the imaging device.
2. Related Art
There have been known an imaging device (e.g., a document camera) for taking an image of a manuscript, a variety of types of materials, and so on placed on a desk and so on as an object, and outputting the image information to an image display device such as a projector, and a personal computer (see, e.g., JP-A-2010-171761 (Document 1)). The document camera described in Document is provided with an automatic focus function for automatically adjusting the focus, and at the same time a zoom function for controlling the magnification ratio of the imaging. In general, as the automatic focus function of the document camera, there is adopted a contrast detection method, which has a simple structure and can be miniaturized. In the contrast detection method, the image of the object is taken to detect the contrast while changing the focus, and the state with the highest contrast is determined as a focused state.
However, in the case of performing the automatic focus process based on the image thus taken as in the case of the contrast detection method, there is a problem that defocus easily occurs when the automatic focus process is performed on the wide-angle side of a zoom function realized by an optical zoom mechanism, and then the shift to the telephoto side is performed. This is because, on the wide-angle side, significant difference in imaging result (the contrast detected and so on) is difficult to occur if the focus is varied in the automatic focus process due to deep depth of field, and it is difficult to perform precise determination on focal state, while on the telephoto side, slight defocus on the wide-angle side appears as significant defocus due to shallow depth of field.